Aminoacyl-tRNA synthetases (AARS) are an important family of enzymes which play a fundamental role in protein biosynthesis in nematodes. The broad objective of this proposal is to understand the phenomenon of neutralizing antibody mediated aminoacylation inhibition of a recombinant Brugia malayi asparaginyl-tRNA synthetase (AsnRS). This work will focus primarly on identification and characterization of the subset of persons from lymphatic filariasis endemic areas who develop neutralizing antibodies, and the immunological properties of neutralizing antibody. This grant proposes three specific aims. First, a two step screening process will identify persons who have spontaneoulsy developed B. Malayi AsnRS:tRNA (Asn) complex from soluble HeLa cell extracts. Secondly, differences or similarities between epitopes recognized by neutralizing and non- neutralizing antibodies will be studied by western blot analysis of a set of overlapping synthetic peptides, corresponding to the full B. malayi AsnRS. Thirdly, the specificity of an in vitro aminoacylation assay will be improved by overproduction and purification of a recombinant tRNA (Asn) gene derived from Caenorhabditis elegans. Long-term, insight from these studies will improve both our general understanding of AARS family in filaria and help to understand the basis for species- specificity of AsnRS neutralizing antibody. The proposed studies also will indicate the basis for cross reactivity between autoantibody and the filarial AsnRS. These goals will simultaneously provide a foundation on which to consider (1) the parasite AsnRS as an excellent target for rational anti-filarial drug design, and (2) the potential role of parasite AsnRS in the induction of autoimmune phenomenon in lymphatic filariasis.